RIO DE JANEIRO/SEOUL, Dec 6 (Reuters) - The world’s largest iron-ore vessel is disabled and could sink in a port where Brazil’s Vale, the world top producer, loads about 10 percent of global supplies of the commodity, shipping agents and the ship’s operator said.

The Vale Beijing, a 361-metre-long vessel that can carry 400,000 tonnes of iron ore, has a leak in a ballast tank, operator STX Pan Ocean said. Shipping agents told Reuters the vessel had ruptured its hull.

The incident at Ponta da Madeira Port near Sao Luis, Brazil, is another blow to a multi-billion-dollar plan by Vale to develop a fleet of 35 giant iron ore carriers to compete with Australian producers for market share in China, the world’s largest iron-ore consumer.

The first in the 400,000 deadweight-tonne class of vessels was blocked by Chinese authorities from docking in China earlier this year.

“Sinking is the worst-case scenario,” said a spokesman for STX Group, the parent of STX Pan Ocean. “But we believe that the situation is not that serious.”

The Vale Beijing is carrying enough iron ore to make the steel for nearly 3-1/2 Golden Gate bridges. If it sank or faced more problems, it could delay operations at the port, which is responsible for nearly 10 percent of the world’s 1 billion tonnes of annual sea-borne iron-ore shipments.

The Panamanian-registered ship, which had been due to depart on Sunday bound for Rotterdam, is expected to be moved to an anchorage area for repairs, Vale said in a statement late on Monday.

“It won’t affect the iron ore supply chain as long as it can get out of the port quickly,” said Graeme Train, a commodity analyst at Macquarie Bank in Shanghai.

“If they can’t and it backs up then there’s a serious problem because you’ve got everything running at 100 percent capacity at the moment.

Vale, along with BHP Billiton and Rio Tinto , control more than two thirds of the global seaborne iron ore market estimated at around 1 billion tonnes a year.

“Ponta da Madeira is a big port. I don’t know how long the ship will be stuck there but it is a big cost for Vale,” said a senior steel raw materials trader at a Swiss trading house.

Engineers from STX Pan Ocean are expected to arrive at the port on Tuesday to investigate the cause of the leak.

The ship is carrying 381,300 tonnes of iron ore, worth $53 million based on Monday’s spot iron ore price.

“If there is a leak between one of the ballast tanks into the cargo holds then it is more serious,” said Roddy Mann, senior iron ore trader at London-based trading house Metalloyd, who added the ship may have to be unloaded for repairs.

GROWING PAINS

The Vale Beijing is the first of eight very large ore carriers (VLOC) costing around $110 million each to be delivered by shipbuilder STX Offshore & Shipbuilding, another unit of STX Group.

STX Group said there would be no delays in deliveries. The next delivery is scheduled for later this month, four ships are due in 2012 and two in 2013.

Still, STX Pan Ocean shares tumbled as much as 6.1 percent on Tuesday in Seoul on concerns its 25-year 7-trillion won ($6.2 billion) contract with Vale may be hit by the incident. STX received the ship two months ago.

Vale has ordered the giant dry-bulk carriers to try to better compete with Australian rival’s BHP Billiton and Rio Tinto, whose main mines are thousands of kilometers closer to China compared with Vale’s mines.

Earlier this year, the Vale Brasil, had to turn around in the Indian Ocean on its maiden voyage after the Chinese government failed to provide permission for the giant ship to dock at Dalian. It went to Italy instead.

“It’s unfortunate timing for Vale,” a ship industry source said.

Chinese authorities could use the incident to argue that the vessels pose safety and environmental risks and thus should be excluded from China’s ports, the source said.

When asked whether Dalian port would consider delaying when Vale’s mega vessels can dock, an official said: “We don’t have such plans as long as the maritime authorities give approval to allow Vale’s entry.”

The port official added Dalian, one of only a few ports in China able to handle the bigger iron-ore vessels, was basically prepared to receive Vale’s carriers.

South Korea’s Daewoo Shipbuilding & Marine Engineering said it was not concerned about the safety of its three VLOCs in operation, following the Vale Beijing incident.